CENG4480 Lecture 05: Sensors Bei Yu byu@cse.cuhk.edu.hk (Latest update: October 21, 2020) Fall 2020 1 / 48
Overview 1. Motion Sensors 1-1. Accelerometer 1-2. Gyroscope 1-3. Compass 1-4. Tilt Sensor 2. Force Sensors 2-1. Force Sensing Resistor 2-2. Strain Gauge 2-3. Flexion (bend) sensors 2-4. Air Pressure Sensor 3. Other Sensors 3-1. Position sensors 3-2. Temperature and humidity 3-3. Optical Sensors 3-4. Hall Effect Sensors 3-5. Kinect Sensors 2 / 48
Overview 1. Motion Sensors 1-1. Accelerometer 1-2. Gyroscope 1-3. Compass 1-4. Tilt Sensor 2. Force Sensors 2-1. Force Sensing Resistor 2-2. Strain Gauge 2-3. Flexion (bend) sensors 2-4. Air Pressure Sensor 3. Other Sensors 3-1. Position sensors 3-2. Temperature and humidity 3-3. Optical Sensors 3-4. Hall Effect Sensors 3-5. Kinect Sensors 3 / 48
1-1. Accelerometer ◮ Electromechanical devices that sense ◮ Static acceleration (gravity) ◮ Dynamic acceleration (vibrations & movement) ◮ Functions: ◮ measure acceleration in one or more directions, position can be deduced by integration. ◮ Orientation sensing: tilt sensor ◮ Vibration sensing ◮ measure acceleration in one or more directions, position can be deduced by integration. ◮ Methods: ◮ Mass spring method ADXL78 (from Analog Device) ◮ Air pocket method (MX2125) 3 / 48
ADXL78 (Mass Spring Method) ◮ Click this online document ◮ Measure the capacitance to create output ◮ Measure both dynamic & static acceleration 4 / 48
ADXL330 Accelerometer for ( X , Y , Z ) Directions ◮ Clik this online document ◮ 3D 5 / 48
2D Translational Accelerometer MX2125 ◮ Clik this online document ◮ Gas pocket type ◮ When the sensor moves, the temperatures of the 4 sensors are used to evaluate the 2D accelerations 6 / 48
Demo: orientation sensing ( https://youtu.be/9NEiBDBXFEQ ) 7 / 48
1-2. Gyroscopes ◮ wiki page ◮ Measure rotational angle Rate Gyroscope ◮ Measure the rate of rotation along 3-axes of X (pitch), Y (roll), and Z (yaw). ◮ Modern implementations are using Microelectromechanical systems (MEMS) technologies. 8 / 48
Gyroscope to Measure Rational acceleration Applications Features ◮ GPS navigation systems ◮ Complete rate gyroscope on a single chip Microelectromechanical systems ◮ Image stabilization (MEMS) ◮ Inertial measurement units ◮ Z-axis (yaw-rate) response ◮ Platform stabilization 9 / 48
1-3. Compass ◮ Philips KMZ51 magnetic field sensor ◮ 50/60Hz (high) operation, a jitter of around 1 . 5 ◦ 10 / 48
Rate gyroscope demo Using Gyroscope compass for virtual reality application in an iphone ( https://youtu.be/VP4-wdMMLFo ) 11 / 48
1-4. Tilt Sensor by OMRON ◮ Click this online document ◮ Detect tilting 35 ∼ 65 degrees in right-and-left inclination 12 / 48
Demo: Tilt Sensing ( https://youtu.be/C6uVrYz-j70 ) One more reference: https://youtu.be/KZVgKu6v808 . 13 / 48
Application – Self Balancing Robot Motion sensors: gyroscope and accelerometer 20cm 35cm by Kelvin Ko ( https://youtu.be/2u-EO2FDFG0 ) 14 / 48
Complementary Filter ◮ Since Gyroscope Accelerometer High Low frequency frequency ◮ Combine two sensors to find output 15 / 48
Complementary Filter (cont.) ◮ θ : rotation angle ◮ τ : filter time constant ◮ s : Laplance operator 16 / 48
Overview 1. Motion Sensors 1-1. Accelerometer 1-2. Gyroscope 1-3. Compass 1-4. Tilt Sensor 2. Force Sensors 2-1. Force Sensing Resistor 2-2. Strain Gauge 2-3. Flexion (bend) sensors 2-4. Air Pressure Sensor 3. Other Sensors 3-1. Position sensors 3-2. Temperature and humidity 3-3. Optical Sensors 3-4. Hall Effect Sensors 3-5. Kinect Sensors 17 / 48
2-1. Force Sensing Resistors ◮ FSR402 ◮ Exhibits a decrease in resistance with an increase in the force applied to the active surface. ◮ Click this online document 17 / 48
Force Sensing Resistor Demo ( https://youtu.be/LQ21lXr6egs ) 18 / 48
Application 1: Walking Robot ◮ Balancing Floor tilled right Floor tilled left upper leg bend left upper leg bend right Neutral position Four sensors under the foot 19 / 48
Four Force sensors under the foot 20 / 48
Application 2: The Nao Robot ◮ uses force feedback at its feet ◮ wiki page ( https://youtu.be/2STTNYNF4lk ) 21 / 48
Application 3: Robot Dog from Boston Dynamics ( https://youtu.be/wXxrmussq4E ) 22 / 48
2-2. Strain Gauge What’s Strain? Amount of deformation of a body due to an applied force. 23 / 48
Strain Gauge (cont.) ◮ Piezoelectric crystal: produces a voltage that is proportional to force applied ◮ Strain gauge: a device for indicating the strain of a material or structure at the point of attachment ◮ Cemented on a rod. One end of the rod is fixed, force is applied to the other end. The resistance of the gauge will change with the force. 24 / 48
Strain Gauge (cont.) Ex: mechanical strain gauge used to measure the growth of a crack in a masonry foundation. 25 / 48
Wheatstone Bridge Wheatstone Bridge R 2 R 3 V O = [ R 3 + R 4 ] · V EX R 1 + R 2 − 26 / 48
Single Element Strain Gauge Sensitive to temperature change. V b gauge Gauge=R+ D R R rod V 0 R R load Out Voltage ∆ R V O = [ R R 2 R + ∆ R ] · V b = [ 4 R + 2 ∆ R ] · V b 2 R − ≈ ∆ R 4 R · V b 27 / 48
Four-Element Strain Gauge ◮ Four times more sensitive than single gauge system ◮ NOT sensitive to temperature change. ◮ All gauges have unstrained resistance R. t1 t2 t1=R+ D RV b rod b2=R- D R V 0 b1 b2 b1=R- D R t2=R+ D R load 28 / 48
Question For four-element strain gauge, calculate V O . V b t1 t2 t1=R+ D RV b rod b2=R- D R V 0 b1 b2 b1=R- D R t2=R+ D R load 29 / 48
2-3. Flexion (bend) sensors Resistance: ◮ 10 K Ω ( 0 ◦ ); ◮ 30–40 K Ω ( 90 ◦ ) https://youtu.be/lEUVlSsAhCg Click this online document 30 / 48
Felixon resistance Demo ( https://youtu.be/m4E5SP7HCnk ) 31 / 48
2-4. Air Pressure Sensor ◮ Measure up to 150 psi (pressure per square inch). 32 / 48
Overview 1. Motion Sensors 1-1. Accelerometer 1-2. Gyroscope 1-3. Compass 1-4. Tilt Sensor 2. Force Sensors 2-1. Force Sensing Resistor 2-2. Strain Gauge 2-3. Flexion (bend) sensors 2-4. Air Pressure Sensor 3. Other Sensors 3-1. Position sensors 3-2. Temperature and humidity 3-3. Optical Sensors 3-4. Hall Effect Sensors 3-5. Kinect Sensors 33 / 48
Infra-red Range detectors ◮ by SHARP (4 to 30 cm) ◮ An emitter sends out light pulses. A small linear CCD array receives reflected light. ◮ The distance corresponds to the triangle formed. http://www.acroname.com/robotics/info/articles/sharp/sharp.html 33 / 48
IR radar using the Sharp range detector https://youtu.be/tStBLAiQaC8 34 / 48
Position Sensors ◮ Rotary ◮ Rotary Encoder ◮ Digital Linear Encoder 35 / 48
Optical Rotary Encoder ◮ wiki page ◮ https://youtu.be/RuIislTGOwA ◮ The light received (on or off) will tell the rotation angle) 3 light receivers Light paths Rotation shaft 3 light emitters Crank shaft sensor 36 / 48
Magnetic rotary encoder ◮ Check the online info ◮ Non touch sensing 37 / 48
Temperature sensors ◮ Click the online document ◮ Directly calibrated in ◦ Kelvin ◮ 1 ◦ C initial accuracy available ◮ Operates from 400 µ A to 5 mA ◮ Less than 1 Ohm dynamic impedance ◮ Easily calibrated ◮ Wide operating temperature range ◮ 200 ◦ C over range ◮ Low cost 38 / 48
Application note connecting to an ADC e.g. ADC0820 or ADC0801 39 / 48
Humidity Sensor ◮ Check the online document ◮ Humidity range (RH) -> Capacitance ◮ BCcomponents 2322 691 90001 : 10–90%RH Dc 40 / 48
Leaf Sensor Alerts When Plants Are Thirsty https://youtu.be/VM4X_fqPPco 41 / 48
Light-to-voltage Optical Sensors ◮ Click the online document ◮ Light-to-voltage optical sensors, each combining a photodiode and an amplifier (feedback resistor = 16 MW, 8 MW, and 2 MW respectively). ◮ The output voltage is directly proportional to the light intensity on the photodiode. 42 / 48
CdS Photoconductive Photocells ◮ Click the online document ◮ Cadmium Sulfoselenide (CdS) ◮ Light sensing using CdS 43 / 48
3-4. Hall effect Sensors ◮ voltage difference across an electrical conductor, transverse to an electric current ◮ A wheel containing two magnets passing by a Hall effect sensor 44 / 48
Application on Magnetic levitation Magnetic levitation Train Model: https://youtu.be/TeS_U9qFg7Y frog levitation https://youtu.be/A1vyB-O5i6E https://youtu.be/XjjBqzilkIc 45 / 48
Hall effect sensors and brushless DC motors Brushless DC motor https://youtu.be/bCEiOnuODac Is it using Hall effect sensor? Don’t known. https://youtu.be/cm0h2Qf3upQ https://youtu.be/JmRkxZT4XhY 46 / 48
3-5. Kinect Sensors https://learn.adafruit.com/hacking-the-kinect https://youtu.be/p2qlHoxPioM https://youtu.be/nvvQJxgykcU https://youtu.be/Brpu30vjCa4 47 / 48
Summary ◮ Studied the characteristics of various sensors ◮ and their applications 48 / 48
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